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MDEV-28111 Redo log writes are being buffered on Linux for no good reason

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In commit 685d958e38b825ad9829be311f26729cccf37c46 (MDEV-14425)
we ended up not enabling O_DIRECT writes on the redo log
by default, because back then, it was slightly slower on
some systems.

With commit a635c40648519fd6c3729c9657872a16a0a20821 (MDEV-27774)
the situation changed. A new test on a NVMe device shows 9%
improvement in throughput and over 15% reduction of latency
when O_DIRECT writes are enabled.

With this change, all the following settings will use O_DIRECT
on InnoDB data and log files:

innodb_flush_method=O_DIRECT
innodb_flush_method=O_DIRECT_NO_FSYNC
innodb_flush_method=O_DSYNC

Before MDEV-14425, log writes were always buffered on Linux.
Between MDEV-14425 and this change, unbuffered log writes
were only enabled for innodb_flush_method=O_DSYNC.
This commit is contained in:
Marko Mäkelä 2022-03-17 12:00:00 +02:00
parent 86820837cb
commit c4c8830709
1 changed files with 4 additions and 6 deletions
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10
storage/innobase/os/os0file.cc
View File

@ -1290,13 +1290,13 @@ os_file_create_func(
#if (defined(UNIV_SOLARIS) && defined(DIRECTIO_ON)) || defined O_DIRECT
if (type == OS_DATA_FILE) {
# ifdef __linux__
use_o_direct:
# endif
switch (srv_file_flush_method) {
case SRV_O_DSYNC:
case SRV_O_DIRECT:
case SRV_O_DIRECT_NO_FSYNC:
# ifdef __linux__
use_o_direct:
# endif
os_file_set_nocache(file, name, mode_str);
break;
default:
@ -1349,9 +1349,7 @@ use_o_direct:
goto skip_o_direct;
}
log_sys.set_block_size(uint32_t(s));
if (srv_file_flush_method == SRV_O_DSYNC) {
goto use_o_direct;
}
goto use_o_direct;
} else {
skip_o_direct:
log_sys.set_block_size(0);